1. Field of the Invention
This invention pertains to methods for preventing evaporation of liquids, and more particularly to such methods which employ surface coatings to form an evaporation barrier between water and the ambient atmosphere.
2. Description of the Prior Art
Various techniques have been devised for reducing water loses due to evaporation from storage reservoirs. These techniques typically involve the formation of monolayers of cetyl, stearyl, and behenyl alcohols. Mixtures of some of these substances are available commercially for use as evaporation suppressants. Certain of these alcohols have been used in large-scale evaporation control work. Early experiments used metering dispensers placed in the water as means of dispersing the alcohols over the water surface. In the largest experiment to date, two crop-dusting airplanes were used to coat a 30,000 acre reservoir with a 1:1 mixture of cetyl and stearyl alcohols; this succeeded in saving an estimated 15 million gallons per day.
Essential to the process of evaporation reduction by monolayer films is the ability to keep such films in a state of compression. Whenever the film is allowed to lapse from this condition, its ability to inhibit evaporation is severely degraded. Evaporation reductions claimed in large-scale efforts typically vary from 16 to 50%.
In view of the mobility of the relatively low molecular weight monofunctional alcohols such as octadecanol, they tend to accumulate on the shore in high wind conditions; therefore, relatively large amounts are required to maintain a hydrophobic monolayer film on the surface of a reservoir. Long chains would function more efficiently since the area covered per hydroxyl group would generally be expected to increase as molecular weight increases; in addition, volatilization of the film and migration to the edge of a tank or reservoir would be reduced.